Not shopping there is the simple solution,
I'd suggest that a far fairer way is to give customers an account #. If you can't keep track of that then be prepared to pay for shipping. In fact I'd also suggest that it's a stupid self defeating policy in any case.
If they're trying to encourage potential customers, as well as returning customers, to purchase more than $35 of stuff, why throw roadblocks in the way? A sale is a sale is a sale.
LV has 'Free Shipping' events a few times each year. They're wide open to the online public.
Generally, if you link to the vendor's website from an email promotion, then the code/discount is automatically applied. If it doesn't, then you have to pay attention and make sure it does. I have found very few vendors that don't automatically apply the code. You just have to be aware.
Shipping cost have gone out of sight. Most of the retailers have realized that their catalog sales are suffering because of that cost. Many have started to offer free shipping as an enticement to catalog shop their inventory.
If I'm not in a hurry for something I take advantage of the "Wish List" feature if available. When they run a free shipping promo then I order. If the tool, part, etc. is unique to the vendor, then you may have to be patient. If the 'wants' are common place then they are available from other vendors and the purchase goes elsewhere.
Sometimes, you just have to think it through. Example; if
I were to buy a Sawstop I would purchase from an out of state vendor. Why? They all drop ship from the factory. The shipping cost is the same no matter where you buy it, and being out of state you avoid the sales tax.
I know, there are pros and cons to this, but on large items it is a huge savings.
Sometimes you just can't avoid the shipping cost. I needed a new Loc Line for the air puffer on my scroll saw. I could get the line and tip from several on-line sources but most wanted $20+ for the part. I found it at Travers for $8. The down side was the shipping was $12. The solution was to stock up on some other things that I needed. When you spread out the cost, that $8 part was still less then half of what the other on-line vendors were charging before shipping, and I got my other items to boot.
I just picked up a Incra 1000HD from Rockler. It was on sale at a price that was $50-60 cheaper then everyone else.
I'm fortunate that the store is only about 10 miles away. It was cheaper to drive down, pay the sales tax and take a side trip to the Woodcraft store a couple of miles down the street, then to mail order it.
You just have to shop smart nowadays. I feel your anger about the promotion code. However, (and no harshness intended) if you are going to take advantage of the codes then it really is up to you to make sure it gets applied. If it doesn't, or is so difficult that it is aggravating, then, maybe it is time to move on to another vendor.